This invention relates generally to the field of hard disc drive data storage devices, and more particularly, but not by way of limitation, to reduction of outgassing from disc drive actuator voice coils.
Disc drives of the type known as xe2x80x9cWinchesterxe2x80x9d disc drives, or hard disc drives, are well known in the industry. Such disc drives magnetically record digital data on a plurality of circular, concentric data tracks on the surfaces of one or more rigid discs. The discs are typically mounted for rotation on the hub of a brushless DC spindle motor. In disc drives of the current generation, the spindle motor rotates the discs at speeds of up to 15,000 RPM.
Data are recorded to and retrieved from the discs by an array of vertically aligned read/write head assemblies, or heads, which are controllably moved from track to track by an actuator assembly. The read/write head assemblies typically consist of an electromagnetic transducer carried on an air bearing slider. This slider acts in a cooperative hydrodynamic relationship with a thin layer of air dragged along by the spinning discs to xe2x80x9cflyxe2x80x9d the head assembly in a closely spaced relationship to the disc surface. In order to maintain the proper flying relationship between the head assemblies and the discs, the head assemblies are attached to and supported by flexures attached to the actuator.
The actuator assembly used to move the heads from track to track has assumed many forms historically, with most disc drives of the current generation incorporating an actuator of the type referred to as a rotary voice coil actuator. A typical rotary voice coil actuator consists of a pivot shaft fixedly attached to the disc drive housing base member closely adjacent the outer diameter of the discs. The pivot shaft is mounted such that its central axis is normal to the plane of rotation of the discs. An actuator bearing housing is mounted to the pivot shaft by an arrangement of precision ball bearing assemblies, and supports a flat coil which is suspended in the magnetic field of an array of permanent magnets, which are fixedly mounted to the disc drive housing base member.
On the side of the actuator bearing housing opposite to the coil, the actuator assembly typically includes a plurality of vertically aligned, radially extending actuator head mounting arms, to which the head suspensions mentioned above are mounted. These actuator arms extend between the discs, where they support the head assemblies at their desired positions adjacent the disc surfaces. When controlled DC current is applied to the coil, a magnetic field is formed surrounding the coil which interacts with the magnetic field of the permanent magnets to rotate the actuator bearing housing, with the attached head suspensions and head assemblies, in accordance with the well-known Lorentz relationship. As the actuator bearing housing rotates, the heads are moved generally radially across the data tracks of the discs along an arcuate path.
Actuator movement is typically controlled by a closed loop digital servo system which serves to accurately position the head over the center of a desired track on a disc surface. This type of servo system obtains head position information from servo fields on the disc. During track-following operations, servo information is read from the disc, and if it is determined that the head is not over the center of the desired track, DC current is sent to the coil in a small amount so as to re-center the head. During track seeking operations, large amounts of current are supplied to the coil so as to provide an initial acceleration to the head, thereby moving it away from a current track toward a desired track. It has typically been an objective in the disc drive industry to decrease seek times in order to increase data access rates. This has been accomplished by making seeks more aggressive; that is, by rapidly accelerating the actuator away from a current track and then rapidly decelerating the actuator as it approaches a desired track. Of course, more aggressive seeks also require more power.
Drive operation can be adversely affected if the drive is subject to contamination. Foreign substances may originate from outside the drive, for example during manufacture if environmental controls are inadequate, or during use if the drive housing is not properly sealed. However, it is also common for these substances to be generated from within the drive during use. Depending upon what materials internal drive components are made of and the temperature to which they are heated, they may release gaseous emissions. This type of contamination is commonly known as xe2x80x9coutgassing.xe2x80x9d Outgassed substances may be deposited on a disc surface, interfering with the ability of a head to read and/or write data from the disc. Disc surface contaminants may also exacerbate static friction, or xe2x80x9cstictionxe2x80x9d, which forms between the head and disc when the drive is not operating and the head is at rest on the disc. In addition to disc contaminants, outgassing may also cause substances to be deposited on other drive components, such as the head, leading to further operational difficulties and eventually drive failure.
One of the primary causes of outgassing is the actuator voice coil. As explained above, during track seeking operations, the head is rapidly accelerated from what is essentially a rest position over an initial track until it reaches a predetermined maximum velocity. It is then rapidly decelerated as it approaches the desired track. In an effort to reduce seek times, seeks have been made more aggressive, requiring more power and increasing the amount of heat generated by the voice coil. If the coil reaches a high temperature for a sustained period, excessive, undesirable outgassing is likely. Such outgassing in turn increases the possibility of drive failure.
A variety of attempts have been made to reduce or eliminate coil-induced outgassing. For example, efforts have been made to select materials for manufacture of drive components which are less prone to outgassing. Recirculating chemical filters have been provided in the drive so as to remove outgassed contaminants from circulation in the drive housing. Others have attempted to coat the coil with materials less likely to outgas when subject to coil temperatures. Still others have attempted to enhance airflow in the coil area in an effort to enhance convection of heat away from the coil. However, none of these methods for reducing outgassing has proved entirely satisfactory for a variety of reasons. Most involve additional costs, for additional parts, more expensive materials or increased manufacturing costs. Moreover, none of these methods address the high power expenditures which is the root cause of the excess coil temperature leading to harmful outgassing.
What the prior art has been lacking is a disc drive in which outgassing is reduced without substantially reducing seek times. It would also be beneficial if such a solution did not involve increased costs associated with additional parts and manufacturing.
Disclosed is a disc drive in which the temperature of an actuator voice coil is regulated so as to prevent outgassing. In a preferred embodiment, coil temperature is calculated at the beginning of each long seek. If the temperature is determined to be at or below a predetermined xe2x80x9csafexe2x80x9d level, temperature rise is not limited and power may be applied to the coil without additional limitations. If, however, coil temperature is determined to be above the xe2x80x9csafexe2x80x9d level, proportional control is used to scale back power generation so as to prevent the coil temperature from exceeding the coil""s specified temperature limit.
Further features and benefits of the present invention will become apparent to one of ordinary skill upon a careful review of the following drawings and accompanying detailed description.